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Symmetry and some questions

65 Views, 6 Replies
03/07/2018 10:26 AM

 

hi, sorry for the following mess 

if i have flow inside a pipe and want to use symmetry condition, 

divide the pipe from the have, shall divide the mass flow rate by 2 ?

 if i have heat flux on the pipe surface, shall i divide the real heat flux value by 2 also?

at meshing what is the recommended wall layer number, is it 10 as in external force flow? 

if i have multiphase flow in the pipe to find the quality at the output, what are bulk values i need

to use to find the quality?

what kind of thermal table do i need to use ?

 

if  the pipe is straight, is it necessary to add entry length as in this article:

http://help.autodesk.com/view/SCDSE/2018/ENU/?guid=GUID-FAF6581B-5FFB-4BAB-91DF-10BA8D35CC62

 

if i add entry length and don't want to add any heat from the pipe surface to this length what to do?

 

you can check the cfz file:

 

https://drive.google.com/file/d/16kvPuFz-9SqvfPQ0gh-7asPNd1w3hlGJ/view?usp=sharing


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Message 1 of 6 ( Views: 65 )

Re: Symmetry and some questions

03/07/2018 11:31 AM

Hi!


eng.abass5 wrote:

 

 

if i have flow inside a pipe and want to use symmetry condition, 

divide the pipe from the have, shall divide the mass flow rate by 2 ?
yes

 if i have heat flux on the pipe surface, shall i divide the real heat flux value by 2 also?
no, if its W/m^2

at meshing what is the recommended wall layer number, is it 10 as in external force flow? 
experts say 5 i think. 10 is better more elements?

if i have multiphase flow in the pipe to find the quality at the output, what are bulk values i need

to use to find the quality?
no idea

what kind of thermal table do i need to use ?

 Thermal table for your material/fluid

 





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Message 2 of 6 ( Views: 59 )

Re: Symmetry and some questions

03/07/2018 11:59 AM

thank you  

 

why when i use very fine meshing setting i can't notice any variation in temperature of the pipe or the fluid

( heat flux at the outer surface of the pipe ) 

just hot spots at the entrance, this was after running 5 iterations which took more than 20 hours.

but it is ok when i use coarser mesh setting !

is there any good meshing practice in case of multiphase?  


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Message 3 of 6 ( Views: 55 )

Re: Symmetry and some questions

03/07/2018 12:03 PM

Hi

20 hours for 5 iterations is crazy much.. Try using adaptive meshing?


https://knowledge.autodesk.com/support/cfd/learn-explore/caas/CloudHelp/cloudhelp/2018/ENU/SimCFD-UsersGuide/files/GUID-5E857F15-5C86-4D5A-A263-AD46DA885073-htm.html

maybe put heatflux at the inside of the tube? or just on the outside of the water? thought it is weird it dosn't take/add heat from the water as it is now

isak


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Message 4 of 6 ( Views: 53 )

Re: Symmetry and some questions

03/07/2018 12:37 PM

hi i ran you simulation with very course mesh, and all your stuff, seems its taking heat from the water;dadadaada.jpg


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Message 5 of 6 ( Views: 46 )

Re: Symmetry and some questions

03/07/2018 1:47 PM

yes, i have the same problem!

fluid here is a saturated refrigerant ,not water.

also i noticed that the velocity is very high , about 150 m/s !!

is there any thing wrong about heat flux boundary condition at pipe surface ?


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Message 6 of 6 ( Views: 41 )